As an optical scanning apparatus that is used in an electrophotographic image forming apparatus, an optical scanning apparatus having the following structure is well known. That is, in the optical scanning apparatus, a light beam that is emitted from a light source is deflected by a rotary polygon mirror, and the deflected light beam is guided to a photosensitive surface of a photoconductor by an optical component, such as a lens and a mirror, to form a latent image on the photoconductor. FIG. 6 is a schematic view of the structural components of an optical scanning apparatus that has hitherto been generally used. Such an optical scanning apparatus is described in detail in the description of embodiments below. In the optical scanning apparatus, when dirt, such as dust, adheres to the optical components in the interior of the optical scanning apparatus, the light beam is blocked by the adhered dust, as a result of which the light quantity of light beam on the photoconductor surface is reduced, thereby causing changes in density to occur. In recent years, as a result of air pollution, the amount of chemical substances and the amount of fine dust in the atmosphere having a size that is less than or equal to 1 μm are increasing. Therefore, a reduction in image quality caused by the dirt on the optical component is becoming a more serious problem than before.
In order to prevent the entry of, for example, dust into an optical scanning apparatus from the outside, for example, the method for sealing a gap at an outer peripheral portion of the optical scanning apparatus by putting a foaming member in the gap, or the method for placing a tape over the gap is often carried out. However, due to, for example, the reasons described below, it is necessary to further improve sealability. In order to meet the recent demand for increasing image forming speed, the rotation speed of the rotary polygon mirror needs to be higher than those of existing products. The rotary polygon mirror that is set in the optical scanning apparatus generates air current by rotating at a high speed. Wind flows in fine spaces that connect the insides of continuously connected air bubbles or places where foaming materials are affixed. At a certain location, air flows from the inside to the outside, and, at another location, air flows from the outside to the inside. The air that flows from the outside to the inside contains fine dust that contaminates the optical component. Therefore, the more the device is operated, the greater the amount of fine dust that enters the inside of the optical scanning apparatus. Consequently, the dust adheres to the surface of the optical component and the inside of a housing. In particular, dust contained in the air current around the rotary polygon mirror adheres to a reflecting surface of the rotary polygon mirror that has rotated at a high speed. That is, the rotation of the rotary polygon mirror causes a Karman vortex and air turbulence to be generated in the vicinity of the reflecting surface of the rotary polygon mirror, as a result of which the air current carrying the dust collides violently with the reflecting surface. As a result, the fine dust that collides with the reflecting surface of the rotary polygon mirror accumulates, and portions of the reflecting surface with which the air current frequently collides become dirty first. Therefore, the reflectivity at the dirty portions of the reflecting surface is reduced. In addition, such a reduction in the reflectivity caused by the dirt reduces the light quantity of light beam that is guided to the photoconductors, as a result of which the density of output images is reduced.
In the optical scanning apparatus, in order to guide the light beam deflected in the optical scanning apparatus to the photoconductor, an opening portion for sending out the light beam from the inside of the optical scanning apparatus to the outside of the optical scanning apparatus is needed. Therefore, the optical scanning apparatus always has the opening portion for allowing the light beam to exit to the outside of the optical scanning apparatus. At the opening portion, in order to prevent contamination such as that described above, primarily, a glass member is attached to the opening portion with a double-sided tape. For example, Patent Literature 1 proposes a structure for bonding and securing part of the glass member to a housing.